This invention relates to a process of preparing a solid controlled release fertilizer composition prepared by the reaction of urea and formaldehyde.
The manufacture of slow release reaction products of urea and formaldehyde for fertilizer applications requires considerable skill to produce the proper degree of polymerization required to achieve the desired fertilizer characteristics. Normally, they are prepared by first reacting urea and formaldehyde at elevated temperatures in an alkaline solution to produce methylol ureas. The reaction mixture is then acidified which causes the methylol ureas to polymerize rapidly to form methylene urea polymers of varying chain length. Such processes are disclosed, for example, in Renner U.S. Pat. No. 3,076,700 and in Czurak et al U.S. Pat. No. 3,705,794.
It is also known that urea-formaldehyde liquid fertilizers may be prepared by the addition of ammonia to the initial alkaline solution of urea and formaldehyde. Such a process is shown, for example, in Formaini U.S. Pat. No. 3,667,736. The Formaini patent in turn uses a urea-formaldehyde reaction product prepared in accordance with the process described in Justice et al. U.S. Pat. No. 3,462,256. The Justice et al and Formaini patents prepare the liquid product by reacting urea, formaldehyde and ammonia until 50 to 80% of the formaldehyde is in the form of methylene groups. This product is then diluted with water, heated and acidified and neutralized to produce a liquid ureaform fertilizer suspension.
My copending application Ser. No. 288,457, filed of even date herewith, discloses a solid fertilizer composition in particulate form prepared by the reaction of urea and formaldehyde having a higher nitrogen efficiency than has heretofore characterized such products. The higher efficiency is made possible by the presence in the reaction product of a high level of polymeric nitrogen, the majority of which is in the form of short chain methylene urea polymers, namely, methylene diurea and dimethylene triurea.
The present invention is directed to a process of preparing a solid controlled release fertilizer composition prepared by the reaction of urea and formaldehyde in which the majority of the polymeric nitrogen is present in the form of such short chain methylene urea polymers. No prior art process known to applicant is capable of preparing the products disclosed in the aforementioned copending U.S. application Ser. No. 288,457.